This invention relates generally to agricultural planters which provide means for monitoring the density of seeds planted, and then automatically adjust the seed dispensing drive in response to variations between the monitored seed density and a desired seed density to maintain the desired seed density. More specifically, there is provided herein an improved means for variably driving the seed dispensing means to assure that the actual number of seeds planted corresponds with the desired seed density.
Recent developments in farming techniques include the use of controlled population planters which automatically monitor the seeds dispensed, compare that number of seeds dispensed to a desired seed dispense rate or density and make changes in the number of seeds dispensed to achieve the desired density of seeds planted. See for example U.S. Pat. No. 3,912,121 issued Oct. 14, 1975 to Steffen wherein such a population control device is adapted to an agricultural planter. However, the planter population control devices available to date utilize hydraulic variable speed seed dispensing drive means. These planters utilize hydraulic motors to either directly power the seed dispensing drives or to provide the torque required to accurately drive the seed dispensing drives at the low RPM's encountered in planting operations. These hydraulic motors are in turn powered by a hydraulic pump which utilizes a servo valve to control the operation of the motor. The motor speed and thus the seed dispensing rate are changed through adjusting the servo valve in response to an appropriate signal received from the population control device. When this type of seed meter drive is adjusted to increase or decrease the seed dispensing rate, the motor often oscillates or else is delayed in responding to the servo valve action. Accordingly, the servo valve and hydraulic motor driving the seed dispensing means do not provide an immediate and accurate change to the seed dispensing rate as is dictated by the population control device. This lag in attainment of desired seed dispense rate is generally encountered as adjustments are made to the planting rate or during the start up at each end of the field.
A further problem can be encountered with the servo valve control due to contaminated hydraulic fluid. Servo valves are sensitive to the small amounts of contamination which can enter the hydraulic system during connection and disconnection of the hydraulic lines. The accuracy with which fine adjustments must be made to the hydraulic motor speed can be lost if such contamination enters the fluid lines. These problems become of concern when small or immediate changes in seed dispensing rate are desired, as for example, when the farmer passes between loam-type soils and sandy soils in which different seed populations are desired.
Therefore, it would be desirable to utilize a mechanical transmission in place of the hydraulic transmission now available with population control devices. However, available mechanical pulley transmissions which can be driven at low RPM's by ground-engaging wheels are not capable of maintaining torque transmission over the full range of pulley speed variation to assure precise seed meter speed changes.